Potential patients will be identified in the cardiac catheterization lab when an intra-aortic balloon pump is placed. Patients who agree to participate in this study will be randomized (they will be selected to receive heparin or not to receive heparin with their intra-aortic balloon pump) by a process that is similar to flipping a coin. Patients will have a 50% chance of receiving heparin and a 50% chance of not receiving heparin. If a patient does not want to participate in the study, his/her cardiologist will decide if the patient will receive or not receive heparin. Intra-aortic balloon pumps have been used with and without intravenous heparin and there is no known increase in complications in patients who do not receive heparin. Risks include bleeding and possible blood clots/decreased blood flow to the leg with the catheter in both groups (due to different medical reasons). The patients in both groups will be monitored closely in the cardiac care unit while the intra-aortic balloon pump is in place to prevent and/or minimize complications.